MTJ (Magnetic Tunnel Junction) elements exploit the magnetoresistive effect (i.e., variable resistance according to the magnetization direction) and are incorporated in Magnetic Random Access Memory (MRAM). An MTJ element has a 3-layer structure including a reference layer, a memory layer, and an insulating layer that forms a tunnel barrier and sandwiched between the reference layer and the memory layer. The magnetization of the reference layer is fixed in one direction, and no inversion takes place in the reference layer even when the write operation is carried out. On the other hand, the magnetization of the memory layer can be inverted during the write operation.
When the MTJ element is processed into a pillar shape, the substrate electrode of the MTJ element is partially etched because the process employs over-etching, and the partially etched electroconductive substance is re-attached on the side wall of the MTJ element. The re-attached substance causes a short circuit of the memory layer and the reference layer. When the memory layer and the reference layer are short circuited, it is impossible to write the data in the MTJ element.